Support stream aliasing of BATCH messages via stream maps

singer_sdk/streams/core.py

@@ -880,6 +880,27 @@ def _generate_record_messages(
                     time_extracted=utc_now(),
                 )
 
+    def _generate_batch_messages(
+        self,
+        encoding: BaseBatchFileEncoding,
+        manifest: list[str],
+    ) -> t.Generator[SDKBatchMessage, None, None]:
+        """Write out a BATCH message.
+
+        Args:
+            encoding: The encoding to use for the batch.
+            manifest: A list of filenames for the batch.
+
+        Yields:
+            Batch message objects.
+        """
+        for stream_map in self.stream_maps:
+            yield SDKBatchMessage(
+                stream=stream_map.stream_alias,
+                encoding=encoding,
+                manifest=manifest,
+            )
+
     def _write_record_message(self, record: types.Record) -> None:
         """Write out a RECORD message.
 
@@ -902,13 +923,9 @@ def _write_batch_message(
             encoding: The encoding to use for the batch.
             manifest: A list of filenames for the batch.
         """
-        self._tap.write_message(
-            SDKBatchMessage(
-                stream=self.name,
-                encoding=encoding,
-                manifest=manifest,
-            ),
-        )
+        for batch_message in self._generate_batch_messages(encoding, manifest):
+            self._tap.write_message(batch_message)
+
         self._is_state_flushed = False
 
     def _log_metric(self, point: metrics.Point) -> None:

tests/core/test_mapper.py

@@ -657,6 +657,9 @@ def get_records(self, context):  # noqa: ARG002
             },
         }
 
+    def get_batches(self, batch_config, context):
+        yield batch_config.encoding, ["file:///tmp/stream.json.gz"]
+
 
 class MappedTap(Tap):
     """A tap with mapped streams."""
@@ -752,6 +755,19 @@ def discover_streams(self):
             "aliased_stream.jsonl",
             id="aliased_stream",
         ),
+        pytest.param(
+            {"mystream": {"__alias__": "aliased_stream"}},
+            {
+                "flattening_enabled": False,
+                "flattening_max_depth": 0,
+                "batch_config": {
+                    "encoding": {"format": "jsonl", "compression": "gzip"},
+                    "storage": {"root": "file:///tmp"},
+                },
+            },
+            "aliased_stream_batch.jsonl",
+            id="aliased_stream_batch",
+        ),
         pytest.param(
             {},
             {"flattening_enabled": True, "flattening_max_depth": 0},

tests/snapshots/mapped_stream/aliased_stream_batch.jsonl

@@ -0,0 +1,5 @@
+{"type":"STATE","value":{}}
+{"type":"SCHEMA","stream":"aliased_stream","schema":{"properties":{"email":{"type":["string"]},"count":{"type":["integer","null"]},"user":{"properties":{"id":{"type":["integer","null"]},"sub":{"properties":{"num":{"type":["integer","null"]},"custom_obj":{"type":["string","null"]}},"type":["object","null"]},"some_numbers":{"items":{"type":["number"]},"type":["array","null"]}},"type":["object","null"]}},"type":"object","required":["email"]},"key_properties":[]}
+{"type":"BATCH","stream":"aliased_stream","encoding":{"format":"jsonl","compression":"gzip"},"manifest":["file:///tmp/stream.json.gz"]}
+{"type":"STATE","value":{}}
+{"type":"STATE","value":{"bookmarks":{"mystream":{}}}}